On Oct 6, 12:36*pm, Tim Wescott wrote:
Vernon wrote:
Gentlemen,

I bought a Hitachi SJ200-022NFU2 model, 3 HP VFD to control my "new"
mill, which has a 2HP 3 phase motor.

This model, a "constant torque" VFD, is versatile and sophisticated,
and contains control options far beyond my needs and expertise.

I have carefully and almost completely read the owner's manual. *The
basic installation is simple enough. *You bring in the 2 legs of 220V
single phase from a 30 amp fuse or breaker, and connect these to
inputs 1 and 3. *You ground the mounted VFD and the mill motor in a
star pattern. *You connect the appropriate 3 outputs from the VFD to
the motor.

You go through an initial programming sequence, setting up certain
basic parameters. *You power up the VFD. *You verify certain that
certain pre-conditions are met and that certain LEDs are on or off on
the keypad. *You take a deep breath, make the sign of the cross, and
press START.

After that the going gets sort of tough. *Here are a couple of things
I don't understand. *I will humbly accept your guidance.

First, it is my understanding that it is possibly fatal to the VFD to
switch the motor on or off from the mill's own on-off switch, or to
otherwise control the mill (instant reverse for example) EXCEPT
through the VFD's programmable circuits.

This leads to the following questions:

1) Do I remove the mill's on-off switch completely or otherwise wire
it permanently in the ON position?
2) Do I similarly wire around the wires going to and from the mill's
FORWARD - REVERSE toggle switch and re-route these wires to the VFD's
programmable inputs/outputs?

There was previously some discussion here about whether a VFD can
adequately handle the mill's instant reverse. *However, upon careful
reading of the manual the VFD does seem to have a programmable "node"
that allows for this. *Apparently this can be tweaked a couple of
ways. *One of these involves installing additional resistors. *Another
SEEMS to provide for programming the injection of a DC current into
the motor to stop it from coasting. *I think these two things are
related but I'm not sure.

I think I can get the thing installed this weekend so that it will at
least start and run. *However, my brain is a lot murkier as regards
these programmable controls.

Thanks to one and all.

Vernon

Disclaimer:

I'm an EE, I've driven motors every which way, but I've never bought a
VFD, so I know theory but not particulars.

First:

If you disconnect the mill's on/off switch, put a big red shutoff button
connected to the VFD power out there. *Make sure you can reach it when
your tie gets caught in the spindle (you _do_ dress formally when you
use your mill, right?).

Second:

A "constant torque" VFD is going to work, more or less, by figuring out
some of the motor's internal state and driving it's voltages
accordingly. *Switching the motor leads is going to confuse the hell out
of it.

Whether or not this damages the VFD is very much a function of whether
the VFD is designed to protect itself. *If you're a circuit designer you
can _always_ make a bullet proof circuit. *You just can't always get
your product line manager to sign up to it ("don't waste time on that,
our customers won't notice that the thing goes up in smoke the way brand
XYZ doesn't").

Third:

If the thing is well designed, and if it has provisions for reversing
the motor and for dynamic breaking, they'll certainly work better than
using the motor switch. *I'd wire them up, and find out if it fits my
definition of "well designed".

Fourth:

Don't forget that emergency stop button. *Sharp spinning metal has an
unfortunate effect on flesh.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says..
See details athttp://www.wescottdesign.com/actfes/actfes.html- Hide quoted text -

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Tim. On behalf of my tender flesh I thank you! V